What is an Index, Primary Key and Foreign Key? When do one use index?

primary key is a candidate key (out of many candidate keys)that is chosen by DB designer to identify entities in an entity set.

simply v can say that it is used to identify a row uniquely.( eg ur roll number is a primary key)

Foreign key- is a column or columns whose values are the same as the primary key of another table.

                 - help in joining two tables

                  -  v can think  it as a copy of primary key from another relational table.

Index key

An index key orders one or more table columns (keys). It has attributes such as being unique or primary, a comparison specification for text columns, and a list of columns which make up the key

Primary key is a candidate key (out of many candidate keys),that is chosen by DB designer to identify entities in entity set.

 Thatis it is used to identify rows uniquely.


Foreign Key is a -column or columns whose values are the same as primary key of aother table.
                          -helps in joining tables
                           - is a copy of primary key from another relational table.

An index key orders one or more table columns (keys). It hasattributes such as being unique or primary, a comparison specification for textcolumns, and a list of columns which make up the key.